1. Technical Field
The present invention relates to a receiving device, a receiving method, a program, and a recording medium, and in particular to a receiving device, a receiving method, a program, and a recording medium capable of improving the reception characteristic.
2. Related Art
In the past, in the wireless receivers, there has been proposed a fractional sampling method or a over sampling method for sampling a symbol signal a plurality of times.
For example, studies have been done on a trade-off between the sampling interval and the characteristic in the direct sequence spread spectrum (DS/SS) modulation method (see e.g., K. J. Kim, S. Y. Kwon, E. K. Hong, and K. C. Whang, “Effect of Tap Spacing on the Performance of Direct-Sequence Spread-Spectrum RAKE Receiver,” IEEE Trans. on Commun., vol. 48, no. 6, June 2000), and on the effect of diversity by fractional sampling in the orthogonal frequency division multiplexing (OFDM) modulation method (see e.g., C. Tepedelenlioglu, and R. Challagulla, “Low Complexity Multipath Diversity through Fractional Sampling in OFDM,” IEEE Trans. on Signal Processing, vol. 52, no. 11, November 2004), and it is obvious that the characteristic is improved by increasing the sampling rate.
Further, in the past, in the receiver of the code division multiple access (CDMA) system, a mechanism for estimating the channel response after over-sampling the received signal and then detecting the optimum despreading timing has been considered (see e.g., Tu Chunjiang, Zhou Xin, Liu Bo-an; Chen Hongyi, “The design of 802.11b WLAN baseband processor,” Proceedings. 5th International Conference on ASIC, 2003, vol. 2, pp. 852-855 October 2003).
As an example of the above, a method of using, for example, sliding correlation (see e.g., US Patent Publications US 2003/0123408-A1 “CDMA Receiving Apparatus,” US 2004/0139466-A1 “Finger Allocation for a Path Searcher in a Multipath Receiver,” and J. Mitsugi, M. Mukai, H. Tsurumi, “Path-search algorithm introducing path-management tables for a DS-CDMA mobile terminal,” Proceedings. The 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Vol. 2, pp. 730-734, September 2002). FIG. 1 is a block diagram of a receiving device 1 for receiving a signal by the channel response estimation method using the sliding correlation.
The received signal is input to a sliding correlation section 11. The sliding correlation section 11 multiplies the received signal by a spread code with a certain phase τ input from a spread code generation section 12. The signal obtained by the multiplication is input to an integrator 13, integrated there for one spread code period, and supplied to a square circuit 14, thus the channel response corresponding to the phase τ is detected. Further, the output of the square circuit 14 is input to a channel response estimation section 15. The channel response estimation section 15 estimates the whole channel response corresponding to other phases than the phase τ.
Further, as another example, a method using correlation can also be cited (see e.g., H. Hamada, M. Nakamura, T. Kubo, M. Minowa, Y. Oishi, “Performance evaluation of the path search process for the W-CDMA system,” Proceedings. 1999 IEEE 49th vehicular Technology Conference, Vol. 2, pp. 980-984, May 1999, and US Patent Publication US 2004/0013218-A1, “Receiving Device and Receiving Method”). FIG. 2 is a block diagram showing the configuration of the receiving device 21 estimating the channel response using the correlation.
The received signal over-sampled by an analogue-to-digital (A/D) converter not shown is input to a decimeter 31, and down-sampled to have an appropriate sampling interval. The output of the decimeter 31 is input to a correlation filter 32, and a correlation process (a matched filter process) is performed thereon. If the received signal has a predetermined correlation, the output of the correlation filter 32 directly represents the channel response, and accordingly, a channel response estimation section 33 estimates the whole channel response based on the output thereof. In this method, the channel response can be estimated in a short period of time.
Further, as another method, a method using a plurality of correlators can be cited (see e.g., U.S. Pat. No. 6,487,193 “Path Searched Device and CDMA Receiver with the Same”). FIG. 3 is a block diagram showing a receiving device 41 capable of estimating a detailed channel response, only when necessary, using two correlation filters.
The received signal is input to the decimeter 51. The decimeter 51 performs decimation on the received signal thus input thereto at two decimation rates, and outputs the decimation output at the higher decimation rate (a lower over-sampling order) to the correlation filter 52 while outputting the decimation output at the lower decimation rate (a higher over-sampling order) to the correlation filter 53. Further, it is arranged to be able to estimate a detailed channel response according to needs by estimating a rough channel response by the correlation filter 52, and then operating the correlation filter 53 with an only necessary delay utilizing the result of the rough channel response estimation. Then, the channel response estimation section 54 estimates the whole channel response based on the results.
It should be noted that these technologies explained with reference to FIGS. 1 through 3 are all for detecting the maximum value of an impulse response in one chip, but not for detecting more than one sample per chip.